Conventionally, an aqueous ink used in the printing field is mainly designed to target an absorbent substrate such as paper and synthetic paper, such as in Patent Documents 1 to 3.
Such an aqueous ink is high in hydrophobicity, and it has been difficult to satisfy the printing quality required to unabsorbent plastic substrate such as polyethylene terephthalate (PET) and a vinyl chloride resin in the market; thus, a solvent ink and an UV-cured type ink has been often used.
However, in recent years, demanded printing technique is to directly write to various unabsorbent substrates used in industrial application by using an aqueous ink that has small influence to the environment and is highly safe to workers.
To this kind of requirement, such as in Patent Document 4, an aqueous ink including resin emulsion has been developed for the usage in the sign graphic field inside and outside houses targeted to an unabsorbent substrate such as vinyl chloride not conventionally used.